1. Field of the Invention
This invention relates to a gas tight light transmitting optical fiber plate and, more particularly, to a process for producing a gas tight light transmitting optical fiber plate.
2. Description of the Prior Art
A highly gas tight light transmitting optical plate, which is used for the face plate of a cathode ray tube, is usually produced by arranging glass fibers or bundles of glass fibers, which are coated with a layer of a glass having a low refractive index, in a die, and compressing the arranged glass fibers at a high temperature to fill the voids between neighboring glass fibers. For producing a light transmitting optical plate having a high vacuum tightness, a high compression must be applied to the glass fibers at a high temperature. This often causes fins or projections from the side faces of the die, thus resulting in an increase in the cost of the light transmitting plate.
In addition, if the voids in the glass fiber bundles are closed, the closed voids are merely stretched in the axial direction of the fibers even with a high compression. Accordingly, if the formed or welded glass fiber product is cut along a plane perpendicular to the axial direction of the glass fiber, cylindrical voids having open ends often result in the product, thus decreasing its vacuum tightness. Furthermore, the conventional process, which includes the step of mechanically compressing the glass fiber bundles at a high temperature, bends and distorts the glass fiber bundles and results in a reduction in the resolving power of the cathode ray tube product obtained.
Another conventional process for producing light transmitting optical fiber plate comprises heating the bundles of the glass fibers surrounded by a material which has a low degree of expansion to a temperature at which the glass fibers are fluidized, causing a high static pressure in the fiber bundles due to the thermal expansion thereof, and thereby forcedly sealing the voids to form vacuum tight glass bundles. This process, however, is not economical and requires intricate apparatus.